Cobalt carbonyl dimer

The major species in the catalytic system with added phosphine is different from that in the system lacking added phosphine. Infrared spectroscopic analyses under steady-state conditions for hydroformylation catalyzed by the phosphine-modified complexes provide no evidence for the accumulation of an acylcobalt complex only phosphine-substituted cobalt carbonyl dimers and hydride complexes are observed.- " ... 

Carbonyiation of butadiene gives two different products depending on the catalytic species. When PdCl is used in ethanol, ethyl 3-pentenoate (91) is obtained[87,88]. Further carbonyiation of 3-pentenoate catalyzed by cobalt carbonyl affords adipate 92[89], 3-Pentenoate is also obtained in the presence of acid. On the other hand, with catalysis by Pd(OAc)2 and Ph3P, methyl 3,8-nonadienoate (93) is obtained by dimerization-carbonylation[90,91]. The presence of chloride ion firmly attached to Pd makes the difference. The reaction is slow, and higher catalytic activity was observed by using Pd(OAc) , (/-Pr) ,P, and maleic anhydride[92]. Carbonyiation of isoprcne with either PdCi or Pd(OAc)2 and Ph,P gives only the 4-methyl-3-pentenoate 94[93]. 

The 3.8-nonadienoate 91, obtained by dimerization-carbonylation, has been converted into several natural products. The synthesis of brevicomin is described in Chapter 3, Section 2.3. Another royal jelly acid [2-decenedioic acid (149)] was prepared by cobalt carbonyl-catalyzed carbonylation of the terminal double bond, followed by isomerization of the double bond to the conjugated position to afford 149[122], Hexadecane-2,15-dione (150) can be prepared by Pd-catalyzed oxidation of the terminal double bond, hydrogenation of the internal double bond, and coupling by Kolbe electrolysis. Aldol condensation mediated by an organoaluminum reagent gave the unsaturated cyclic ketone 151 in 65% yield. Finally, the reduction of 151 afforded muscone (152)[123]. n-Octanol is produced commercially as described beforc[32]. 

Use of Co2(CO)8 in reactions involving 1,2-propadienes remains for the most part unexplored. It has been reported that terminal 1,2-propadienes react with Co2(CO)8 to form unidentified complexes, and that excess 1,2-propadiene is polymerized concurrently [30]. It has also been reported by Nakamura that a novel dimeric complex 54, in which a carbonyl ligand is connected to the central carbon of 1,2-propadiene, is produced by the reaction of 1,2-propadiene itself with Co2(CO)8 (Scheme 23) [31]. However, unlike the well-known chemistry of alkyne-Co2(CO)6 complexes, these 1,2-propadiene-cobalt carbonyl complexes have rarely been applied in synthetic reactions, probably due to their high activity in catalyzing the polymerization of 1,2-propadienes [32]. 

Synonyms dicobalt octacarbonyl cobalt carbonyl cobalt tetracarbonyl dimer... 

Similar acetylene addition reactions take place with bis-cydopentadienylnickel carbonyl dimer (93). Changing from carbonyl to cyanide ligands seems to allow the formation of a true vinyl derivative. Thus, potassium pentacyanocobaltate, which may react as a dimer with a cobalt-cobalt bond (20), reacts with acetylene to give the adduct XV (31). The product was thought to be the trans isomer, but the data were not conclusive. 

The foregoing implies that the addition of an electron to cobalt carbonyl (or the dimer) leads to the formation of the cobalt carbonyl anion. If this is indeed the situation, then it should be possible to convert dicobalt octacarbonyl to the anion by an external source of electrons as well as by a homomolecular disproportion. Such a conversion was achieved by shaking a benzene solution of dicobalt octacarbonyl with sodium amalgam ... 

Not only is it possible to convert dicobalt octacarbonyl to cobalt carbonyl anion but an as yet incomplete study indicates that it is possible to convert the anion to the dimer by the reversal of Equation (2). The steps in this conversion can be visualized as occurring by electron transfers in a homomolecular disproportionation ... 

CatalystY of cobalt-carbonyl reactions can ntiUze tbe water solnbiUty of the salt and the hydrocarbon solnbihty of the metal metal dimer. Ion pairing is important in the disproportionated metal complexes, and traces of water in organic solvents can not only serve as catalysts for this reaction but can also influence the equilibrium position by stabilizing the ionic products. 

CARBONYLHEXACARBONYLDI-, (CO-CO) COBALT OCTACARBONYL COBALT TETRACARBONYL COBALT TETRACARBONYL DIMER DI-MU-CARBON-YLHEXACARBONYLDICOBALT DICOBALT CARBONYL DICOBALT OCTACARBONYL OCTACARBONYLDICOBALT... 

Metal carbonyl dimers are prepared with biscyclopentadienyl linked ligands. The following sequence of reactions is utilized to prepare cobalt dimers E... 

For Co, having one electron less than Ni, one finds that Co(CO)4 can accept one additional electron. This is the reason why dimerization occurs giving the stable [Co(CO)4]2 complex, but bonding of Co(CO)4 with an hydrogen atom can also occur. Because of the stability of the Co(CO)4 anion (18 electron rule), the hydrogen atom in the hydrogen cobalt carbonyl complex has an acidic character ... 

The cobalt carbonylates of Cd and In gave mixtures of dimers at the same concentrations at which Zn[Co(CO)4]2 also gave dimer mixtures. However, both catalysts also responded to Lewis acid cocatalysis. The mercury compound in itself was also unselective, but gave Binor-S in the presence of BPa O(C2H6)2. The catalyst In[Co(CO)4]3 did not produce a norbornadiene trimer. Concerted trimerization, though not completely unlikely, would require all three norbornadiene molecules in... 

Although it would appear that cobalt carbonyl thus should behave as a typical binuclear catalyst, it produced only a nonspecific mixture of dimers and no Binor-S (Table III) (52). 

The reaction of metal carbonyl dimers with silicon hydrides also probably involves an initial oxidative addition step. Chiral silyl-cobalt and silyl-manganese carbonyl complexes have been obtained through the reaction of optically active organosilicon hydrides with metal carbonyls65 68 (equation 15 and 16). Phosphine-substituted cobalt complexes were similarly obtained by reaction of a chiral hydrosilane with Co2(CO)6L2 [L = PPh3, P(OPh)3, P(c-C6Hn)3]69. 

There has not been much research in the area of metal-catalyzed reactions of thiiranes, which are sulfur analogues of epoxides. It has been shown that chlorodicarbonylrhodium(I) dimer can catalyze the homogeneous desulfurization of thiiranes to olefins [35]. This reaction is stereospecific and proceeds for thiiranes having aliphatic, aromatic, ether, and ester substituents (Equation (6.8)). This chemistry contrasts with that observed with cobalt. At room temperature, when 2-phenylthiirane, was treated with CO (latm), CH3I, KOH, CgHg, tetrabutylam-monium bromide, and a catalytic amount of cobalt carbonyl, fl-mercapto acid, was... 

Synonyms Cobalt carbonyl Cobalt octacarbonyl Cobalt tetracarbonyl dimer Dicobalt carbonyl Dicobalt octacarbonyl Octacarbonyidicobalt... 

---